Two-feed &#34;x&#34; band antenna



1953 w. s. PARNELL EIAL 2,627,020

TWO-FEED "X" BAND ANTENNA Filed May 28. 1949 TRIGGER MODULATOR n IRANSMITTER GENERATOR osc|1 A ToR Fig.1.

P -ru Enocv'uue ATR corn-Rm. Tues PATH 6 Lac-J4me ATR Conrnzon. fus 3O I William s. Parnell a Jot n W. Taylor, Jr.

ATTORNEY Patented Jan. 27, 1953 UNITED STATES T 9F F I CE? Ti VO-FEED X BAND. ANTENNA Application May 28, 1949, Serial-Nor 95,954

l Claims. 1.

Ourinvention relates to systems for the detection ofdistant-objects and, more particularly, to such systemsfor determining the direction and distance ofobjects. It concerns itself with systemsin which theantenna lobes are switched periodically and direction is determined by comparing signals received on the two lobe positions. Apparatus in accordance with our invention is designed primarily for use in guided missiles. Lobe switching apparatu for detecting distant objects constructed in accordance with the prior art is typified by Beck Patent 2,409,183. In such apparatus, wave guides are used as the antenna elements and a single reflector is used for both guides; transmission occurs out of one wave guide at a time. The transmit antenna pattern are identical to the receive antenna, patterns, except forthe effect of the lobe switching mechanism between the time the pulse is transmitted and the time it is received. This mechanism of the prior art alternately tunes and detunes the wave guides. In accordance with the teaching ofthe prior-art, it is mechanically controlled and the switching rate is low. Since the signal reflected from targets, ships, and planes in particular, fluctuates as much as 30 db, the more rapidly the signals from left and right beams can be compared, the less chance the returning signal has to vary; Further, when the transmit and receive patterns are identical and, in each of the lobe positions are coincident, the pattern which results from plotting the products of the vectors of one pattern by the vectors of the other, which weshall define as the directional sensitivity pattern, will have a beam separation for the two lobepositions, that is'an angular separation of the peaks of thepatterns, equal to that of the transmit and receive patterns. This beam separation of the directional sensitivity patterns is larger'than desired because of the geometrical limitation of the feed structure. We have found that this condition causes'excessive loss of effective power when ontarget; that is, when the received energies on each of the lobes are equal. Such loss is a decided dis advantage in a guided missile.

Prior art apparatus for detecting objects of another type is exemplified in the Hoffman Patent 2,424,984. In Hofimans-apparatus; the antennas are of the dipole type. Transmissionoccurs from both antennaelements simultaneously and then reception alternately at one .or the other antenna: elements. The lobe switching iszeffected electronically. The direction; of the receive pat-- terns: depend on the difference in electrical lengths of the transmission paths to the two an- 21 tennar elements and, therefore, VEJIl-GSEflSsthl-ZIITfiHS- mitterfrequency drifts; Because of thisivariation, the angle. between the lobes and; therefore, the accuracy of the lobe switchingsmechanismds critically dependent on frequency.

In guided missile work, itis necessary that the auto pilots or servo systems which control the flight of the missile receive stable error information, that is, stable information as to deviation from the target. A the servo sees it, fluctuations in strength of returning signals by reasonof the physical characteristics of. the target. arethe same as fluctuations. in antenna. angle. The servo,- therefore, respondssimilarlyto signalsiof both type and the flight. is unstable. It isdesirable, therefore, to make as rapid as possible comparisons between the energies received over the two receive patterns or lobes;

It is accordingly an objectof our inventionto provide a radar systemwhich shallhave the compactness, the accuracy and the freedom 'f'rom frequency sensitivity indispensable toguided missile use.

An ancillary object of our invention is to pro- I vide alobe switching system independent offrequency, in which the switching between lobes shall be effected electronically.

Another ancillary object of our'in-ventionis to provide a lobe switching system of" the small dimensions indispensable to guided missiles, which shall have a high degree of directional sensitivity and atthe sametime shall transmit a maximum of energy in the on-target direction A further ancillary objectof our invention is to provide a lobeswitchingsystem suitable for operation at high frequencies Whichshall include lobes.

A still further object of ourinvention isto-provide a -rad'ar impulse system of the lobe switched type which shall besuitable for operation at-high frequencies, shall havenhigh directional sensitivity and shall be capable of transmitting asmax imum of energy in'the-on-target direction;

In accordance with our invention; we provide an antenna lobeswitchingsystemhavingelectronic switching between lobes inwhichthe lengths of the transmission paths to the-antenna elements are not critical. Control means'isaiso provided for transmitting simultaneously out of both antenna elementsand then-receiving energy on onlythe left antenna-element, transmitting again. .out of both antennaelementsend'this time=receiving energy only: on the right-antenna element: This=control means-may be ofany gen-- eral type but in accordance with the specific as- 3 pects of our invention include a multivibrator of the Eccles-Jordan scale of two type and discharge devices responsive to the plate output of the multivibrator and located in or alongside the transmission paths from the transmitter and receiver means.

In the specific practice of our invention, the transmission paths to the antenna elements and the antenna elements themselves are wave guides. When using these wave guides, the effective operation of the equipment is not affected by changes in frequency during operation.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however both as to its organization and its method of operation, together with additional objects and advantages thereof, will be understood from the following description of specific embodiments thereof when read in connection with the accompanying drawing, in which:

Figure 1 is a schematic diagram of apparatus and circuits of an embodiment of our invention;

Figure 2a is a diagram showing the transmit and receive lobe patterns of the apparatus shown in Fig. l; and

Figure 2b is a diagram showing the directional sensitivity patterns resulting from the transmit and receive patterns shown in Fig. 2a.

Referring to Figure 1, the drawing of the apparatus comprises four main parts. The first two main parts are the transmitter means I and the receiver means 3. The third main part is an antenna structure 5 to which energy is conveyed from the transmitter means. This antenna structure 5 likewise receives the reflected energy and control means 6 are provided for blocking transmission of received energy through only one of the transmission paths 7 and 8 to the receiver means 3 after the transmission of impulse energy, blocking the transmission of received energy to the other transmission path i or 8 to the receiver means 3 after the next impulse is transmitted, thus alternately blocking the transmission paths 1 and 8. This control means 6 also blocks transmission of energy to the receiver means 3 during the instants of transmission of impulse energy from the transmitter means i. The control means 6 for accomplishing this constitutes the fourth main part.

The transmitter means I consists of a trigger generator 9, a modulator II and a transmitter oscillator i3, which in the preferred practice of our invention may be a magnetron. This transmitter means I may be of any standard type known in the art. The receiver means 3 is likewise or" standard type.

The third main part, the antenna structure 5, comprises a reflector I5, antenna elements I! and i9, and transmission paths 1, 8, 2| and 23, leading to the antenna elements H and It. The reflector |5 in the specific embodiment of our invention is a parabolic reflector. This parabolic reflector. l5 has a focal point 24, an axis 25, and a vertex 26. Each of the antenna elements i1 and |9 comprise a wave guide having apertures 28 and 29, respectively, facing the reflector it. Two transmission paths 2| and 23 connect the transmitter means I to the antenna elements I? and I9. Two transmission paths 7 and 8 also connect the receiver means 3 to the antenna elements H and I9. In the specific embodiment of our invention, these four transmission paths 1, 3, 2| and 23 are wave guides. The transmission paths 2| and 23 have means for blocking return 4 to the transmitter of energy transmitted through them. In the specific embodiment of our invention, this means for blocking the return of energy through the two transmission paths 2| and 23 to the transmitter means I from the antenna elements ll and I9 are ATR (anti transmisser-receiver) tubes 30 and 3|, one in each path. When these ATR tubes 3|] and 3| are nonconductive they constitute an open circuit in the transmission paths 2| and 23 blocking flow of energy along the transmission path. When the transmitter means I is triggered these tubes 3|] and 3| break down for the period of the high energy transmitted pulse so as to permit energy to flow to the antenna elements H and I9 from the transmitter means Discharge devices 33 and 35 which form a part of control means 5 are provided for blocking the transmission of transmitted and received energy through the transmission paths 8 and 1 under the proper circumstances. In the specific embodiment of our invention, these devices are TR. (transmitter-receiver) tubes 23 and 35. When either of these tubes 33 or 35 breaks down, it short circuits its corresponding path preventing flow of energy through it to the receiver means 3.

The ATR tubes 3! and 3| are located a distance of /4 wave length along the wave guide away from the junction points a and a of the guides 1 and I! and 8 and i9, respectively. The TR tubes 33 and 35 are located a distance of wave length along the wave guide away from the junction points a and a When these tubes 39, 3|, 3?- and 35 are so located substantially no R. F. energy is reflected within the wave guides I, 8, 2| and 23, either on transmission or reception. The ATR tubes 33 and SI are located on the sides of the transmission paths or wave guides 2| and 23 and when energy from the transmitter means is transmitted through the wave guides 2| and 23, the ATE tubes 38 and 3| fire and allow the passage of the energy to the antenna elements |l and |9. The TH tubes 33 and 35 are located within the wave guides 7 and 8 which connect the receiver means 3 to the antenna elements it and I9. These TR tubes 33 and 35 on being fired prevent the transmission of energy through the wave guides l and 8. Therefore, when energy is transmitted from the transmitter means these TR tubes 33 and 35 fire and none of this transmitted energy can get to the receiver means 3.

The received energy, that is, the energy that is returned after having been reflected off an object, is not suflicient to fire either the TR or ATR tubes 30, 3|, 33 or 35. Thus provision has to be made for allowing the received energy to be picked up or received by the receiver means 3. This is taken care of by control means c which alternately fires the two TR tubes 33 and 35.

The control means 5 or the fourth main part comprises a multivibrator 3i, two control discharge devices 39 and M having anodes es and 35, cathodes il and 48, and control electrodes 5| and 53, respectively, and the two TR tubes 33 and 35 hereinbefore mentioned. The multivibrator 3"! is responsive to the transmitter means i and more particularly to the output 0:? the trigger generator 9. The multivibratcr 3? shown is an Eccles-Jordan scale of two mu1tivibrators; however, any suitable multivibrator may be used. The multivibrator 3, comprises two discharge devices 55 and 5?, each discharge device 55 and 51 having anodes 5s and ti, oath odes 63 and 65, and control electrodes t? and 69. The control discharge devices 55 and 5? are pattern. for transmissionresponsive to: the plate. outputs: of" the multivibrator 31, there being a connection from the anode 59 of'the.firstmultivibrator dischargedeviceiEtto-the-control electrode.5:l cf the control discharge device 39 and a connection fromthe anode 6| of the second multivibrator discharge device 51430. the control electrode 53 of theother control discharge. device 41; The. anodes: 4.3 and 45. of thetwo: control discharge devices .39. and 4 I are; connected: to. the two. TR. tubes. 33 and. 35 through: current". limiting resistors- TI and I3: as shown;

Referring to. Figuresqza: and b" ofgthe drawin the patterns IOI and H23 represent the reception lobes and. pattern. I05 represents the radiation represents-simultaneoustransmission out oiiboth of the antenna elements (one lobe; H159- and then alternate, reception of reflected energy by first onezantennaelement I"! or 19; and then the. other (lobes: I -17 and: I013) The angle Awhichu the; axes, I61 and. IE8 of these directional. reception-patterns IIH and. I 03 each makev with; the axis: IgII ct transmitted energy may beapproximately determined from the physical disposition ,of the antenna elements III-arid- I 9 with respect to the: vertex 25' of, the parabolic reflector I. To achieve maximum range, or radar sensitivity, it is; desirable that angle A; be, as small as practicablestill maintaining lobe-separation.

Angles can be varied-by changing thephysical disposition: of theantenna elements ll and" I9 with respect to the vertex 25 of the paraboliczrei'lector I5 (as was explained in the preceding paragraph) thatis, by; utilizing a reflector having a, larger or smallerfocal distance. The angle A would become smaller'i-f the-antenna elements I? and I9, which are;l0cated' at the focal point, were mounted farther from' the parabolic rcfiector I 5-in other words, if a refiectorwere used having a largerfocal length. However, by mounting the antenna elements I and I9 further awayfrom the parabolic reflector I5, either a. larger diameter parabolic reflector or more directive feedshave to be used so. as to prevent loss of energy overthe edge ofthe dish. Moreover,.even if space requirements would permit a larger parabolic reflector, this would make the receive and directional sensitivity patterns lei, I33, H3 and H5 more directive (have a smaller beam width), and the cross-over level of the receive and directional sensitivity patterns Ifii; I03, H3 and II5; which determineradar sensitivity, wouldremain essentially constant. The other alternative, more directive feeds; r,equires larger feed apertures and, hence, wider feed spacing, Andwhenthefeedspacing is increased; the; beam separation ofv the receive and directionalsensitivity patterns IBI, m3, i I3; and. H5 isiincreased to. the. same .-value. with which. we began. Tousumm-arize theparabola sizegthe focal. length, and the feedv separation all have aneffecton the cross-over-level of the patterns. However, the interrelationsbetween these variables is. such. thatthe, maximum cross-overlevel using. two feeds is independent of them. After a. maximum. has beerrattained, changing one; of the variables necessitates a changezinone ofthe others which counteracts theeifect: on the crossoven level. In the specific embodimentof. our invention; a. primary; consideration: is making the feed apertures 28 and 29 as small as possible so that. th eilect on theaperture. of thezrerlector I5 will be negligible. The choice of plain waveconfiguration guide feeds to attain this and the; limitation; of parabola diameter. completely specify all other dimensions; Therefore; the. antenna; elements I11 and; I 9' have: their apertures 2 8 and 29* respectively located atthe focal point 24 of the parabolicrrefiector I5- and. both antenna: elements I! and:.I.9ihave their sidesclose to the'a-xis 25'ot'the reflector I5.

The transmit pattern I05 represents the variationiinyamount of energy impinging on a target as a. function of its bearing. The receiver patterns. IIlI. and M3 in turn representthe amount of: energy which will be: picked up as afunction ofjthe direction from which energy comes. Therefore, the patternsof directional sensitivity H3 and II5,the energy picked up from atarget asafunctionof its bearing iS determined bythe product of the transmit energy in: any direction by the receive energy; in ,thatdirectionthat is, graphically: the product. of the patterns;

The directional sensitivity is graphically, the product; of the patterns, Inoth'er words if the receivedintensity; is R14 0 and. the transmit, T 4 0, the-directional signal R'Tze; The vector-prod not would give R7120;

It shouldbe noted thatif thereceive patterns IiII' and IIISare separatedbythe angle 2A,,the directional sensitivity lobes- I I 3rand- H5- are separated by only half this angle, assuming that both transmit and receive patterns I 05, IIJI and I031 are identical. in shape. This can be easily seen by considering. the point: of; intersection of onereceive pattern with;the transmit pattern. Forangles greatergorless-than that corresponding-to this point, thevector, determined by-one pattern decreasesfaster than the vector determined by the other increases, so the maximum product of directional sensitivity occurs at this angleA/Z or B.

Assume a target I i l is located in the direction shown. A signal whose intensity is indi-catedby the-radius vector to the point I I9 frompoint I 2I in the direction Illis received bythe antenna when operating in accordance with the right lobe. A signal whose intensity is indicated by the radius vector to the point I23 is receivedby the antenna when operating according to left'lobe. The. differencebetween these. two vectors determines the error signal, the indication of how far the antenna structure-Eispointing away'from the target I I1. The intersectionpoint' I25" of the two directional sensitivity patterns H3 and Ilfiidetermines both (A) the intensity of the. signal returned when the antenna structure 5 is on-target and (B) the rate ofchange of error signal as a function. of target bearing. We define (A) as the radar sensitivity, the ability of the radar equipment to pick; up weaksignals. We define (B) asxthe error sensitivity, the accuracy to which the antenna: structure 5. may be. pointed atthe target; Changing-the cross-over lever I25 will increaseone sensitivity at the expense of the other. It is generally considered that the best compromise between radar sensitivity and error sensitivityis accomplishedby having the crossover; level athalf power or. 3 db down from the peak.

We have found that in a system according to our invention in which the transmit lobe is maintained fixed and the receive lobe is switched, the maximum radar sensitivity isattainable while maintainingefiec tive directionalsensitivity; The improvement in sensitivity over prior-art'systems mayiresultin an increassin range as high" as 20%.

The operation of the apparatus shown in Fig ure 1 is as follows:

Energy is transmitted out of both antenna elements I1 and I9. Then reflected or received energy is received on the left feed or antenna element I! with the right antenna element I9 blocked by means of a TB tube 35 in conjunction with the remainder of control means 6. Energy is then again transmitted out of both antenna elements I1 and I9. This time the left antenna element I1 is blocked by means of the TR tube 33 in conjunction with the rest of control means 6 and the energy is received on the right antenna element I9. This operation is continually repeated receiving energy alternately on the left and the right antenna elements I! and I9 respectively.

Pulses from the magnetron I3 split at the wave guide junction of transmission paths ZI and 23 fire all the ATR and TR tubes 33, 3I, 33 and 35 respectively, and then proceed out both feeds or antenna elements I! and I9 in phase to the parabolic reflector I5. The energy is reflected ofi the parabolic reflector I5 and forms the radiation pattern I05 shown in Figure 2. Received signals returning through these antenna elements I! and iii are blocked from each other and from the transmitter means I by the ATR tubes 33 and 3i and then proceed through the unfired TR tube 33 or to the receiver means 3. The two TR tubes 33 and 35 are alternately fired by means of the multivibrator 3'! and the two control discharge devices 39 and 4| so that after the transmission of a pulse, received energy can reach the receiver means 3 through only one of the transmission paths 1 or 8, the other path being blocked by the TR tube 33 or 35. When the next pulse is transmitted the multivibrator 31 trips and the control discharge device 39 or ill which is made conductive by the multivibrator 31 blocks the transmission path I or 9 that had previously allowed the transmission of received energy through it and unblocks the other transmission path i or 3 to the receiver means 3. Thus the reception will be as shown by the two lobes Ii3I and I93 in Figure 2.

The multivibrator is such that the outputs taken off of the anodes 59 and SI of the two discharge devices and 51, forming a part of the multivibrator 31 are 180 degrees out of phase. The multivibrator 31 is responsive to the output of the trigger generator 9 and the control discharge devices 39 and ll are responsive to the outputs of the multivibrator 31. As a pulse is sent out from the trigger generator 9 to operate the modulator II and magnetron I3 for transmission purposes, a like pulse in phase with the pulse to the modulator I I and magnetron I3 causes the multivibrator 3'! to trip in one directionor the other. Since the outputs of the multivibrator 3'! are 180 degrees out of phase, only one of the control discharge devices 39 or 4| will conduct at any one time. When the multivibrator 31 receives another pulse from the trigger generator 9 the opposite discharge device 39 or 4H conducts. The discharge devices 39 and 4| fire alternately, one being in the fired condition all the time. Each of the TR tubes 33 and 35 are responsive to the output of one of the control discharge devices 39 or 4|. Thus when one of the control discharge devices 39 or 3| is conducting the TR tube 33 or 35 that is responsive to its output will have been fired serving to block the transmission of energy in that transmission path 1 or 8. When the other control discharge 39 or 4| is conducting, the other TR tube 33 or 35 will be fired thus blocking the transmission of energy in its transmission path I or 3.

It is to be understood by those skilled in the art that any suitable transmitter or receiver means I or 3 can be used with the apparatus shown.

It is to be further understood by those skilled in the art that any suitable multivibrator could be used in the place of the one 31 shown. Variations in multivibrators might include switching at some other time than at transmission, operation of discharge devices 39 and M for short periods of time to cover targets within a limited variation of range, etc.

It is to be further understood by those skilled in the art that any suitable control means could be substituted for the control discharge devices 39 and 4| shown.

It is to be further understood by those skilled in the art that any suitable blocking means could be used in place of the ATR and TR tubes 33, 3 I, 33 and 35 respectively shown.

It is to be still further understood by those skilled in the art that any suitable reflector can be used in the place of the parabolic reflector I5 shown. The antenna elements I! and I9 can also, if desired, be located further apart, that is a certain distance away from the focal line 25 of the reflector I5.

It is to be still further understood by those skilled in the art that any other suitable type of feed structure such as polyrods, slot antenna, etc., may be used in the place of the plain wave uides.

Although We have shown and described certain specific embodiments of our invention, we are fully aware that many modifications thereof are possible. Our invention, therefore is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. A radio impulse system, comprising a transmitter, a receiver, a concave reflector having a focal point, a pair of antenna elements substantially equally spaced from said focal point, each of said antenna elements comprising a wave guide having an aperture facing said reflector, a first wave guide section connecting said transmitter to one of said antenna elements, a second Wave guide section connecting said transmitter to the other of said antenna elements, a third wave guide section connecting said receiver to said first wave guide section, and a fourth wave guide section connecting said receiver to said second wave guide section.

2. A radio impulse system, comprising a transmitter, a receiver, a concave reflector having a focal point, a pair of antenna elements substantially equally spaced from said focal point, each of said antenna elements comprising a wave guide having an aperture facing saidrefiec'tor, a first wave uide section connecting said transmitter to one of said antenna elements, a second wave guide section connecting said transmitter to the other of said antenna elements, a third wave guide section connecting said receiver to said first wave guide section, a fourth wave guide section connecting said receiver to said second wave guide section, and control means synchronized with said transmitter for alternately Blocking said third and fourth wave guide sec- 1ons.

3. A radio impulse system, comprising a transmitter, a receiver, a concave reflector having a focal point, a pair of antenna elements substantially equally spaced from said focal point, each of said antenna elements comprising a wave guide having an aperture facing said reflector, a first Wave guide section connecting said transmitter to one of said antenna elements, a second wave guide section connecting said transmitter to the other of said antenna elements, a third Wave guide section connecting said receiver to said first wave guide section, a fourth Wave guide section connecting said receiver to said second Wave guide section, control means synchronized with said transmitter for alternately blocking said third and fourth Wave guide sections, and means responsive to transmission of energy from said transmitter for blocking said third and fourth wave guide sections while unblocking said first and second Wave guide sections.

4. The invention in accordance with claim 3 characterized by the part of said means responsive to the transmission of energy from said transmitter for blocking said third and fourth wave guide sections being located one-half wave length from the junctions of said first and third, and. second and fourth wave guide sections, respectively, and by the part of said means respon- 10 sive to transmission of energy from said transmitter for unblocking said first and second wave guide sections being located one-quarter wave length from said junctions, respectively.

WILLIAM S. PARNELL. JOHN W. TAYLOR, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,408,055 Fiske Sept. 24, 1946 2,412,159 Leeds Dec. 3, 1946 2,412,315 Brown Dec. 10, 1946 2,412,991 Labin u Dec. 24, 1946 2,415,933 Brown Feb. 18, 1947 2,422,184 Cutler June 17, 1947 2,422,190 Fiske June 17, 1947 2,446,819 Fyler Aug. 10, 1948 FOREIGN PATENTS Number Country Date 582,419 Great Britain Nov. 15, 1946 589,958 Great Britain July 4, 1947 

